MCUs have served the requirements for a broad range of applications for many years. With the advent of lower pin-count offerings, microcontrollers enable embedded processing to become available to a wide variety of applications including automobile electronics to home appliances. However, as the need for more functionality offered by these lower pin-count MCUs increases, the amount of overhead pins needed can become an important factor. Overhead pins can be defined as all pins not directly available for the MCU user for the application, including power supply and ground supplies, dedicated pins for isolation, reset pins, as well as test pins.
For embedded programmable MCU devices, overhead pins typically include all the device pins necessary to interface to the device for software/hardware tools related to debugging and programming the device and its firmware, including support for the in-house testing needs of the semiconductor manufacturer. Traditionally, overhead pins have been dedicated pins at the cost of additional overhead. In one arrangement, some overhead pins can be multiplexed with the existing functional pins of the device. Although pin multiplexing helps reduce the overall pin count, pin multiplexing does not allow for all functional pins to be readily available during debug. Pin multiplexing can therefore make hardware and firmware development challenging.